The long-term goals of the proposed program are to further the understanding of the mechanism of cellular immunity with an emphasis on lymphocyte mediators. These substances are elaborated by antigen or mitogen activated lymphocytes and are thought to play an important part in mediating cellular immunity or hypersensitivity. Our emphasis has been and will continue to be on one of these, migration inhibitory factor (MIF), which is measured by its ability to inhibit the migration of normal peritoneal macrophages out of capillary tubes and which appears to enhance the defense capacity of these cells. The specific goals of the proposed work are: Further investigation of the role of carbohydrate containing components on the macrophage surface as part of the receptor site for MIF and characterization of this receptor moiety and its relation to other macrophage membrane components. Further investigation of the role of macrophage associated esterases as a possible control mechanism of the MIF macrophage interaction and characterization of these esterases. Purification of MIF employing such refined purification methods as sucrose density gradient electrophoresis,$ sucrose density gradient isoelectrofocussing and affinity chromatography and investigation of the role of the two recently detected MIF species, pH3-MIF and pH5-MIF. BIBLIOGRAPHIC REFERENCES: Remold, H.G. and Mednis, A.: Decrease of three lysosomal enzymes in guinea pig macrophages activated by lymphocyte mediators. Inflammation 1:175, 1976. Remold, H.G.: Chemical treatment of macrophages increases their responsiveness to migration inhibitory factor (MIF). J. Immunol. 118:1, 1977.